The present invention relates to a setting device for a throttle valve or for a feed device of an internal combustion engine with idling speed-of-rotation control, in which the feed device is connected to a displacement rod, and is pretensioned by a return spring. Furthermore, there are provided a first adjustable stop and a second fixed stop for an actuating lever of the feed device, the second fixed stop limiting the range of adjustment of the first stop for a minimum setting of the feed device.
As is known, the idling speed-of-rotation is controlled in order to improve the operating behavior of an internal combustion engine and to reduce the injurious components in the exhaust gases. For this purpose there is ordinarily provided an electric or pneumatic setting device which so sets a stop of a feed device, such as for instance a throttle valve or a control rod of an injection pump, that a desired idling speed-of-rotation is obtained. The operating conditions under which an internal combustion engine operates differ greatly and, accordingly, different desired values result for the idling speed-of-rotation, for instance upon cold start in winter, under high load due, for instance, to attached servo-devices and air-conditioning systems, when the internal combustion engine is warm or is operating with low load, etc. The range of adjustment of the stop must be correspondingly large in order to assure at all times the proper running of the internal combustion engine. Regulation of the idling speed-of-rotation to a minimum value has also become important for the reason that, in order to obtain favorable fuel consumption and emission values, the lowest possible idling speed-of-rotation is desirable and, in this way, there is present a possibility of variations in the idling speed-of-rotation, which makes a rapid resetting of the idling speed-of-rotation necessary.
At present, mechanical but with increasing frequency electronic, idling speed-of-rotation controls are being installed. These controls in the normal case assure, as desired, a sufficient but not excessively high idling speed-of-rotation corresponding to the existing operating conditions. For example, they control electric or pneumatic setting devices which shift the stop of the feed device to a suitable position. If a defect arises in these controls, assurance must be had that the idling speed-of-rotation is in such case set back to a small value. Otherwise, for example, in the case of automatic transmissions there may be an unintended forward movement, for example upon crawling of the vehicle, which may result in dangerous situations.
Upon the failure of an electronic control, however, an unfavorable idling speed-of-rotation can be brought about. If, namely, upon the failure, the stop is shifted in the direction of the minimum idling speed-of-rotation, then the minimum opening of the throttle valve may not be sufficient to assure satisfactory operation of the internal combustion engine and a throttling or standstill of the engine may take place.
German OS 35 24 911 describes a setting device of the aforementioned type for the throttle valve of an internal combustion engine in which the angular adjustment range is about 10.degree.. No measure is disclosed for establishing an idling speed-of-rotation which assures reliable operation of the internal combustion engine upon the failure of the idling speed-of-rotation control.
German patent 29 49 884 describes a setting device for a feed device of an internal combustion engine with idling speed-of-rotation control which comprises a valve element which has a first set of openings for normal operating condition and a second set of openings of smaller cross-section for an abnormal operating condition. If a disturbance occurs, the openings of the first set are closed by simple means by spring action while the set of second openings provides an idling speed-of-rotation which assures operation of the engine.